What is the test for substantive due process in civil law?

Courts " 'ha[ve] always been reluctant to expand the concept of substantive due process because guideposts for responsible decisionmaking in this unchartered area are scarce and open-ended.' [Citation.] By extending constitutional protection to an asserted right or liberty interest, we, to a great extent, place the matter outside the arena of public debate and legislative action." (Washington, supra, 521 U.S. at p. 720.) Thus, our substantive due process analysis "must begin with a careful description of the asserted right, for '[t]he doctrine of judicial self-restraint requires us to exercise the utmost care whenever we are asked to break new ground in this field.' " (Reno v. Flores (1993) 507 U.S. 292, 302 (Reno).)